Voters in Washington state on Tuesday rejected a proposed carbon tax that would have been the first such levy in the nation.

The policy would have been an effort to fight climate change by mandating that companies using or selling fossil fuels pay taxes equal to $15 per metric ton of carbon, an amount that would rise in future years. The money would have paid for clean air and water projects, as well as community health initiatives.

The proposal was one of the most aggressive attempts to fight climate change on the state level. Supporters saw the vote as a crucial test of whether carbon pricing can get support in the United States.

A handful of countries have carbon taxes, as do some Canadian provinces, but no U.S. state does.

The battle over Washington’s carbon tax got international attention and national funding during the campaign season. Supporters spent at least $12 million, and opponents spent more than $25 million.

Washington Gov. Jay Inslee (D), a potential 2020 presidential candidate, led the campaign to implement the tax, arguing that it was a reasonable method to make polluters pay for the damage they cause to the climate.

Conservatives and fossil fuel companies pushed back aggressive and argued that a tax would hurt struggling families and businesses when energy companies pass it along. Opponents said it would have cost an average household $440 in the first year.

The tax would have risen by $2 each year until Washington’s annual emissions reached 25 percent below 1990 levels.

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The CO2 Coalition was established in 2015 as a 501(c)(3) for the purpose of educating thought leaders, policy makers, and the public about the important contribution made by carbon dioxide to our lives and the economy.